1. Field of the Invention
The present invention relates to a toner to be used for formation of images based on an electrostatic photographic process such as for copiers, facsimiles, and printers. The present invention also relates to a method for producing the toner and an image forming method using the toner.
2. Disclosure of the Related Art
An electrophotographic image forming method includes a transferring step for transferring an image onto the surface of an image transferring member, a fixing step for fixing a toner image on the surface of the image transferer, and a cleaning step for removing a residual toner remaining on the surface of the image bearing member after the transferring process,
In recent years, forming of higher-quality images is increasingly required. In particular, to achieve formation of highly fine color images, researches aimed at making toner particles have smaller particle diameters and forming toner particles in a spherical shape have been under way. Making toner particles having smaller particle diameters allows improving dot-reproductivity, and forming toner particles in a spherical shape allows improving developing property and transferring property of toner. Since it is very difficult to produce a spherically shaped toner having smaller particle diameters by kneading and pulverizing method, polymerized toners produced by suspension polymerization method, emulsion polymerization method, or dispersion polymerization method are being employed.
However, when a spherically-shaped toner having small particle diameters is used, it raises the following problems during cleaning of a residual toner remaining on an image bearing member.
Conventionally, as a unit for removing a residual toner remaining on an image bearing member after a transferring process, blade cleaning system has been used because of its simple structure and excellence in removing ability of a residual toner. A cleaning blade system removes a toner while sliding on and rubbing the surface of an image bearing member, however, the edge portions of the cleaning blade are deformed due to frictional resistance to the image bearing member. Therefore, a microscopic clearance is induced between the cleaning blade and the image bearing member because the smaller toner particle diameter, the easier the toner particles enter the clearance. The nearer to a spherical shape the entered toner has, the smaller the rolling frictional force is. Thus, the entered toner particles start to roll in the clearance between the image bearing member and the cleaning blade and slip through the cleaning blade, thereby resulting in cleaning failures.
Then, a proposal is presented to address troubles concerning cleaning ability of a residual toner while improving the developing property and transferring property of a toner by controlling the shape of the toner such that the toner has a somewhat different shape from a spherical shape.
For example, Japanese Patent Application Laid-Open (JP-A) No. 11-060739 discloses a method in which in the process where a plurality of primary particles were associated with and fused to each other in a solution containing primary particles having thermal adhesiveness and at least one solvent to thereby produce secondary particles, the required agitation power per unit volume is varied according to the average toner particle diameter of particles. However, associating completely solid primary particles with each other, not associating oil droplets with each other, needs raising the temperature of the components to make the primary particles thermally fused to each other. Therefore, the method has problems with low-productivity and widening a particle size distribution.
Japanese patent Application Laid-Open (JP-A) No. 06-282105 discloses a method for producing toner particles for developing electrostatically charged images which includes adding inorganic oxide fine particles to a color resin dispersion in which resin fine particles containing at least a pigment are dispersed in an aqueous medium to flocculate color resin fine particles, heating the color resin dispersion to fusion-bond the flocculated color resin particles, thereby forming associated particles. However, the method needs raising the to temperature of the color resin dispersion to the glass transition temperature or more to associate primary particles with each other, and thus it is difficult to control the particle size distribution.
Japanese Patent Application Laid-Open (JP-A) No. 2005-049858 discloses a method for producing a toner containing toner resin particles which contain a resin (a) and a filler (b), in which toner resin particles have a volume average particle diameter of 3 μm to 10 μm, and a shape factor (SF-2) of 110 to 300; each of the toner resin particles has an outer shell layer (S) containing at least a part of the filler (b); and the outer shell layer (S) has a thickness of 0.01 μm or more and a half or less of the maximum inscribed circle radius of the cross-sectional surface of the particles. However, the toner production method has problems that the shape of toner cannot be sufficiently controlled, and toner particles may be formed in a spherical shape.
In addition, Japanese Patent Application Laid-Open (JP-A) No. 2005-070680 discloses an apparatus for producing a toner for electrophotographic image formation, which is provided with a continuous emulsifying apparatus and is used for a method in which a toner composition containing at least a resin, a colorant, and a releasing agent is dissolved or dispersed in an organic solvent and the solution or dispersion is continuously emulsified in an aqueous medium. The toner production apparatus is provided with a unit which allows varying the accumulation volume of emulsified portions
In such a process for forming toner particles to have a somewhat different shape from a spherical shape, when particles after being subjected to an emulsification process are unevenly and indefinitely shaped, the level of how the shearing force is applied to the toner particles is uneven in the process of forming of toner particles to have a somewhat different shape from a spherical shape, Thus, the obtained toner particles differently shaped from spherically shaped toner particles are also unevenly formed. When the shape of toner particles differently shaped from spherically shaped toner particles is uneven, the cohesion force between toner particles is reduced in a fixing process. This adversely affects fixing of image to cause an increase in lower limit fixing temperature of the toner.